1. Field of the Invention
The present invention relates to a circuit arrangement for testing a passive bus network comprising stations connectible to a coaxial cable segment via media adapter unit, the stations realizing the data packet exchange via the coaxial cable segment with the carrier sense multiple access with collisions detection (CSMA/CD) method.
2. Description of the Prior Art
As transmission media, passive bus networks of the type set forth above comprise coaxial cables to which the stations are connected via passive media adapter units. Due to the attenuation and the limited band width of the coaxial cable, the length of the coaxial cable segment is presently limited to about 500 m. The stations are connected to the media adapter units via special transmit/receive cable which are constructed as stranded lines whose length is limited to about 50 m for the same reasons.
The passive bus network operates according to the CSMA/CD principle. Included is that every station receives data packets from all other stations by way of the respectively appertaining media adapter unit. The term "multiple access" means that all stations of this passive bus network have equality of access to the bus network without central control. Transmission from the station via the correspondingly-appertaining media adapter can only be carried out when no data information are being exchanged via the passive bus network. The simultaneous transmission of a plurality of stations leads to what is referred to as collision. This situation is recognized by a collision recognition circuit in the media adapter unit of each tansmitting station by way of level monitoring at the transmission medium and leads immediately to the abort of the transmission of data. After a waiting period stochastically-defined in duration, the station again undertakes attempts at transmission.
For testing such passive bus networks, involved isolation and reflection measurements with time reflectometers are currently carried out only at the coaxial cable segment in order to be able to identify the proper operating condition of the transmission circuit. Given these types of test, no statements regarding the operating function of the stations connected to the coaxial cable segments are possible.